1. Field of the Invention
This invention relates to a process for producing an optical transmission fiber.
2. Description of the Prior Art
Many of the optical transmission fibers in the prior art are made of optical glass and show considerable light absorption losses since such transmission fibers are more liable to contain impurities as compared with those made of a fused silica and are restricted with respect to the purities of the raw materials and the melting process therefor. Another example of a known optical transmission fiber is a fused silica clad type fiber. This clad type fiber is produced by depositing a fused silica layer doped with metal oxides on the inner surface of a fused silica pipe to increase the index of refraction above that of a fused silica, sintering the same in an oxygen atmosphere, heating and melting for spinning to eliminate the cavity of the fused silica pipe. The fiber is thereafter annealed in an oxygen atmosphere to completely oxidize the metal component.
This heat-treatment weakens the strength of the fiber.